Combine harvesters are machines to engineered to travel through agricultural fields at harvest time harvesting crops. They typically include a self-propelled vehicle upon which a harvesting head is mounted. The harvesting head extends across the front of the combine harvester and severs the stalks of the crop plants close to the surface of the ground.
The harvesting head severs at least a portion of the plants from the ground, gathers the severed portions together, and conveys them into the body of the combine harvester itself for further processing.
The combine harvester performs three basic processing functions: threshing, separating, and cleaning. The combine harvester also stores the grain until it can be unloaded from the combine harvester.
The threshing and separating are performed by a cylindrical rotor disposed inside a closely spaced concave. The concave is a hollow and generally cylindrical-shaped structure that surrounds the rotor.
A narrow gap is provided between the rotor and the concave. The severed crop matter is introduced into this gap at a forward end of the rotor and concave. As the rotor rotates against the stationary concave, it threshes the crop, and separates the grain from the material other than grain (MOG) such as leaves, stalks, husks, and cobs.
The frictional drag between the rotor and the concave is significant, particularly when the gap between the rotor and the concave is filled with crop material.
For optimum performance, it is beneficial that the rotor rotates at a constant speed. The load on the engine changes, however, making it difficult to keep the rotor operating at a constant speed. As the combine harvester moves up and down hills, or encounters heavier crop that forms a thicker layer between the rotor and the concave, the power required to rotate the rotor can increase substantially.
In a typical combine harvester, a direct mechanical connection (i.e. the power transmission path) with a fixed rotational speed ratio is provided between the engine and the rotor. Furthermore, the rotor and the engine run at constant relative speeds with respect to each other. In normal operation, the operator operates the combine at its maximum possible speed to harvest a crop as fast as possible. The engine is controlled to operate at a constant and (typically) high speed. The speed of the engine is typically around 2000 to 2200 RPM when the combine harvester is operating at full speed.
There are drawbacks to this conventional mode of operation. For one thing, operating at maximum engine speed prevents the engine from operating in its most fuel-efficient operating zone, which is typically (for internal combustion engines) anywhere from 50% to 80% of the engine's maximum operating speed.
As a result, even when the load on the engine is relatively light, the engine is kept operating at a high speed that is fuel-inefficient. The engine could be operated at a lower and more fuel-efficient speed. However, due to the direct connection between the engine and the rotor, the rotor would also run slower, and the ground speed of the combine harvester would have to be reduced to prevent the rotor from being overloaded. Thus, operating the engine in a more efficient region at a proportionately lower speed requires that productivity be decreased by a similar proportion. There would be little need for this, however, if there were a way to switch the engine to a lower, more efficient speed, while maintaining a high rotor speed.
What is needed, therefore, is a new combine harvester drive system for driving the rotor of a combine harvester that will permit the engine speed to automatically change from a high-speed/fuel inefficient region to a lower speed/fuel-efficient region while keeping the rotational speed of the rotor substantially constant.
It is an object of this invention to provide such a system.